1. Field of the Invention
The present invention relates to a method of tertiary or enhanced oil recovery from certain subterranean oil reservoirs and, more particularly, to a method for recovering oil from sandstone reservoirs through the injection of a specially prepared fluid as the drive mechanism wherein the binder of sand grains are dissolved into a true solution thereby releasing the oil trapped in the capillarities and discontinuous solution channels provided a bi-lateral flow of the oil and drive process fluid from the formation to a production system for producing wells.
2. Description of the Prior Art
It is now recognized by the oil fraternity that three main physical and chemical factors that must be taken in account in order to recover residual oil are capillary retention forces, mobility relationships and reservoir heterogeneity. Capillary retention forces operate when oil and water are present within a porous rock system. The rock wetting phase, usually water, traps the fluid contents obtained in single pores, capitillarities, and discontinuous solution channels of the vortex of sand grains. Mobility relationships are determined by the surface tension between the oil and the water. The heterogeneity of a reservoir is unlike any other reservoir in its physical and chemical composition and even within a single reservoir the heterogeneous composition has a marked variance from one point to another.
Scientists have come to the conclusion that the earth was formed from a "big bang" episode and that the earth formed from a collection of this cosmic dust and debris. As a quantity of unconsolidated crust of the earth became engulfed in a vast fire and the products of which provided the tools which consolidated and shaped various sedementary beds that comprised the present crust.
This hypothesis has considerable support from known and established chemical action and reaction by continued analysis of the mineral content of the sedementary beds. These beds contain silicon dioxide, a widely distributed non-metallic compound, and the carbonates of base forming metals and/or alkaline earth metals. Further evidence under the hypothesis indicates that all elements were originally created through mutation from a common substance. Accordingly, the first chemical reaction would be the oxidation. Continuing, the next step would be continued reaction with the carbon dioxide to form carbonates. For example, it is well known that calcium oxide and carbon dioxide form the insoluble carbonate of calcium. Further reaction with an excess of carbon dioxide form soluble calcium bicarbonate. This form remains until its deposition is effected by the evaporation of the liquid vehicle. Such evaporation is typical of that which occurred on beaches and sandbars of the ancient seas. The evaporation decomposes the bicarbonates by release of the CO.sub.2 and reverts them to insoluble carbonate form. The analysis of oil well cores, in fact, shows the matrix or cementitious material of the rock to be insoluble carbonates. In some instances this carbonaceous matrix amounts to as much as 50% of the formation bulk.
Of current interest, is the production of oil from underground oil bearing formations by what is called "tertiary or enhanced recovery methods." Such methods are typically instituted after a primary production program and a secondary program using water as a drive mechanism to force the oil to a producing well. These two oil recovery methods are generally conceded to leave large amounts of residual oil in place. This unrecovered oil is caused by many factors including retention forces of the capillarities and discontinuous solution channels, the surface tension in the oil and water together with the viscousness of the oil itself and the heterogeneity of the reservoir. Other factors detrimental to the efficient recovery of the residual oil are improper oil well completions, incompatibility of the driving fluid to the characteristics of the oil bearing formation, use of excessive pressures that cause channeling and other minor techniques not conducive to the efficient recovery operation.
Accordingly, tertiary or enhanced recovery techniques have been developed that show promise of recovering a large amount of the residual oil which would be lost after a secondary oil recovery operation had reached economic limits. Typically, tertiary or enhanced recovery techniques require certain additives to the propelling force that will release the oil trapped in the capillarities and at the same time reduce the surface tension and also the heterogenous nature of the producing formation. In some instances single well injection production methods are proposed and prior to the start of a tertiary or enhanced oil recovery operation certain production wells will be injected with the processed fluid and is to be included within the scope of this invention.
Water drive or water flooding is the most widely used secondary recovery technique. Here, residual oil is recovered by injecting water into one or a series of wells where it is forced vertically and horizontally toward one or more producing wells thereby driving the oil ahead of the water. Although a water drive process has certain economic advantages, channeling or gravity segregation of the oil and water caused by the water drive process interferes with efficient displacement of oil from large segments of the formation.
An advanced tertiary oil recovery method was described in my U.S. Pat. No. 3,135,326 entitled "Secondary Oil Recovery Method". My prior method utilized the injection of various banks of fluids to aid in oil recovery. In certain water wet sand formations a different method may be used and is the basis of this application.